1. Field of the Invention
This invention relates to an electrically rewritable and non-volatile semiconductor memory device (EEPROM).
2. Description of the Related Art
A NAND-type flash memory is well-known as one of EEPROMs. The NAND-type flash memories are, in consideration of the property variations generated in the manufacturing processes, shipped after writing various voltage setting values used in write, erase and read operations into a ROM fuse area in the chip based on the result of the wafer test. When users use the memories, the fuse ROM data are automatically read out every power-on reset time. As a result, suitable voltage setting values are set in registers and used in accordance with write, erase and read operations (refer to, for example, JP-A-2001-176290).
Explaining in detail, what are written in the ROM fuse area and read out to be held in the registers are data such as voltage trimming data used as control data of a voltage generating circuit used for generating various voltages. That is, assuming that a voltage range is set as an adjustable range, voltage trimming data are stored in the registers to be used for suitably setting the output voltages of the voltage generating circuit.
As the chip size is shrunk and data multiplication are progressed in a flash memory, and the number of voltage trimming data becomes larger, there will be increased not only the capacity and area of the ROM fuse area but also the capacity and area of the registers used for storing the voltage trimming data read from the ROM fuse area. In consideration of this situation, there have been provided some ideas for reducing the capacity and area of the ROM fuse area and registers with arithmetic operations introduced for reducing the number of trimming data to be held (for example, JP-A-2007-87513, JP-A-2006-344280 and JP-A-2007-179594).
On the other hand, users are not allowed to freely rewrite the ROM fuse area. Therefore, in case the memory properties are varied and the most suitable voltages are varied as a result of that the flash memory is used for a long time, there is no options in the conventional flash memories for dealing with the situation.